Due to the relatively limited amount of unsaturation present in commercial butyl rubber, including the commercially significant halogenated butyl rubbers, attempts have recently been made to prepare butyl rubbers containing a greater degree of unsaturation. These attempts culminated in the significant discovery that the dehydrohalogenation of halogenated butyl rubber produces a butyl rubber containing conjugated diene unsaturation. This significant discovery, which has proven to have a substantial impact upon the elastomer business, is embodied in two recent U.S. patent applications; namely, Ser. No. 228,728, filed Feb. 23, 1972 in the name of Francis P. Baldwin now U.S. Pat. No. 3,775,387 issued Nov. 27, 1973, directed to a process for preparing such conjugated diene butyl, and Ser. No. 228,727 also filed on Feb. 23, 1972, in the name of Francis P. Baldwin and Alberto Malatesta, now U.S. Pat. No. 3,816,371 issued June 11, 1974 directed to the conjugated diene butyl produced thereby, both of which are assigned to Esso Research and Engineering Company, the assignee of the present application. While specific portions of the disclosures of both of these applications will be referred to herein, these applications are incorporated herein by reference, particularly with respect to the teachings regarding the specific processes for producing such significantly improved butyl rubbers.
The butyl rubber containing conjugated unsaturation which is taught in these applications may be represented by the general formula: ##STR1## where n + 1 represents the number of isoolefin units incorporated in the butyl rubber, and m represents the number of initial diolefin units present, substantially as isolated units. Furthermore, as also described therein, other structures can be present, and, indeed, they may predominate. For example, when the precursor halogenated butyl has the structure: ##STR2## the following structure will be present: ##STR3##
These products thus represent a composition of matter comprising a copolymer consisting of from 85 to 99.5% by weight of an isoolefin having from 4 to 7 carbon atoms, combined with 15 to 0.5% by weight of a conjugated diolefin having from about 4 to 14 carbon atoms, containing conjugated diene unsaturation. Preferably, the composition comprises a copolymer of isobutylene and isoprene, a major portion of the isoprene units combined therein having conjugated diene unsaturation. In addition, the various structures possible regarding these compositions are set forth in copending application Ser. No. 465,479, filed 4/30/74, incorporated herein by reference.
As stated above, the revelation of these processes for preparing butyl rubbers containing such conjugated diene unsaturation has had a significant impact upon this industry.
Methods for improving upon these processes have, however, been deemed most desirable.